X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=mm%2Freadahead.c;h=aa1aa23452355067af9d62179cd41d62c64e68fc;hb=8051be5e614f3e3feccbe9e06b50e0b889740a93;hp=229788884010d18a8dba50f65dbcfe7bb37df744;hpb=eb2be189317d031895b5ca534fbf735eb546158b;p=safe%2Fjmp%2Flinux-2.6 diff --git a/mm/readahead.c b/mm/readahead.c index 2297888..aa1aa23 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -3,7 +3,7 @@ * * Copyright (C) 2002, Linus Torvalds * - * 09Apr2002 akpm@zip.com.au + * 09Apr2002 Andrew Morton * Initial version. */ @@ -17,19 +17,6 @@ #include #include -void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page) -{ -} -EXPORT_SYMBOL(default_unplug_io_fn); - -struct backing_dev_info default_backing_dev_info = { - .ra_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE, - .state = 0, - .capabilities = BDI_CAP_MAP_COPY, - .unplug_io_fn = default_unplug_io_fn, -}; -EXPORT_SYMBOL_GPL(default_backing_dev_info); - /* * Initialise a struct file's readahead state. Assumes that the caller has * memset *ra to zero. @@ -44,6 +31,42 @@ EXPORT_SYMBOL_GPL(file_ra_state_init); #define list_to_page(head) (list_entry((head)->prev, struct page, lru)) +/* + * see if a page needs releasing upon read_cache_pages() failure + * - the caller of read_cache_pages() may have set PG_private or PG_fscache + * before calling, such as the NFS fs marking pages that are cached locally + * on disk, thus we need to give the fs a chance to clean up in the event of + * an error + */ +static void read_cache_pages_invalidate_page(struct address_space *mapping, + struct page *page) +{ + if (page_has_private(page)) { + if (!trylock_page(page)) + BUG(); + page->mapping = mapping; + do_invalidatepage(page, 0); + page->mapping = NULL; + unlock_page(page); + } + page_cache_release(page); +} + +/* + * release a list of pages, invalidating them first if need be + */ +static void read_cache_pages_invalidate_pages(struct address_space *mapping, + struct list_head *pages) +{ + struct page *victim; + + while (!list_empty(pages)) { + victim = list_to_page(pages); + list_del(&victim->lru); + read_cache_pages_invalidate_page(mapping, victim); + } +} + /** * read_cache_pages - populate an address space with some pages & start reads against them * @mapping: the address_space @@ -65,14 +88,14 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages, list_del(&page->lru); if (add_to_page_cache_lru(page, mapping, page->index, GFP_KERNEL)) { - page_cache_release(page); + read_cache_pages_invalidate_page(mapping, page); continue; } page_cache_release(page); ret = filler(data, page); if (unlikely(ret)) { - put_pages_list(pages); + read_cache_pages_invalidate_pages(mapping, pages); break; } task_io_account_read(PAGE_CACHE_SIZE); @@ -110,15 +133,12 @@ out: } /* - * do_page_cache_readahead actually reads a chunk of disk. It allocates all + * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all * the pages first, then submits them all for I/O. This avoids the very bad * behaviour which would occur if page allocations are causing VM writeback. * We really don't want to intermingle reads and writes like that. * * Returns the number of pages requested, or the maximum amount of I/O allowed. - * - * do_page_cache_readahead() returns -1 if it encountered request queue - * congestion. */ static int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, @@ -187,6 +207,7 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp, if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) return -EINVAL; + nr_to_read = max_sane_readahead(nr_to_read); while (nr_to_read) { int err; @@ -208,35 +229,19 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp, } /* - * This version skips the IO if the queue is read-congested, and will tell the - * block layer to abandon the readahead if request allocation would block. - * - * force_page_cache_readahead() will ignore queue congestion and will block on - * request queues. - */ -int do_page_cache_readahead(struct address_space *mapping, struct file *filp, - pgoff_t offset, unsigned long nr_to_read) -{ - if (bdi_read_congested(mapping->backing_dev_info)) - return -1; - - return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); -} - -/* * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a * sensible upper limit. */ unsigned long max_sane_readahead(unsigned long nr) { - return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE) + return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE) + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2); } /* * Submit IO for the read-ahead request in file_ra_state. */ -static unsigned long ra_submit(struct file_ra_state *ra, +unsigned long ra_submit(struct file_ra_state *ra, struct address_space *mapping, struct file *filp) { int actual; @@ -325,6 +330,59 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra, */ /* + * Count contiguously cached pages from @offset-1 to @offset-@max, + * this count is a conservative estimation of + * - length of the sequential read sequence, or + * - thrashing threshold in memory tight systems + */ +static pgoff_t count_history_pages(struct address_space *mapping, + struct file_ra_state *ra, + pgoff_t offset, unsigned long max) +{ + pgoff_t head; + + rcu_read_lock(); + head = radix_tree_prev_hole(&mapping->page_tree, offset - 1, max); + rcu_read_unlock(); + + return offset - 1 - head; +} + +/* + * page cache context based read-ahead + */ +static int try_context_readahead(struct address_space *mapping, + struct file_ra_state *ra, + pgoff_t offset, + unsigned long req_size, + unsigned long max) +{ + pgoff_t size; + + size = count_history_pages(mapping, ra, offset, max); + + /* + * no history pages: + * it could be a random read + */ + if (!size) + return 0; + + /* + * starts from beginning of file: + * it is a strong indication of long-run stream (or whole-file-read) + */ + if (size >= offset) + size *= 2; + + ra->start = offset; + ra->size = get_init_ra_size(size + req_size, max); + ra->async_size = ra->size; + + return 1; +} + +/* * A minimal readahead algorithm for trivial sequential/random reads. */ static unsigned long @@ -333,34 +391,26 @@ ondemand_readahead(struct address_space *mapping, bool hit_readahead_marker, pgoff_t offset, unsigned long req_size) { - int max = ra->ra_pages; /* max readahead pages */ - pgoff_t prev_offset; - int sequential; + unsigned long max = max_sane_readahead(ra->ra_pages); + + /* + * start of file + */ + if (!offset) + goto initial_readahead; /* * It's the expected callback offset, assume sequential access. * Ramp up sizes, and push forward the readahead window. */ - if (offset && (offset == (ra->start + ra->size - ra->async_size) || - offset == (ra->start + ra->size))) { + if ((offset == (ra->start + ra->size - ra->async_size) || + offset == (ra->start + ra->size))) { ra->start += ra->size; ra->size = get_next_ra_size(ra, max); ra->async_size = ra->size; goto readit; } - prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT; - sequential = offset - prev_offset <= 1UL || req_size > max; - - /* - * Standalone, small read. - * Read as is, and do not pollute the readahead state. - */ - if (!hit_readahead_marker && !sequential) { - return __do_page_cache_readahead(mapping, filp, - offset, req_size, 0); - } - /* * Hit a marked page without valid readahead state. * E.g. interleaved reads. @@ -370,32 +420,62 @@ ondemand_readahead(struct address_space *mapping, if (hit_readahead_marker) { pgoff_t start; - read_lock_irq(&mapping->tree_lock); - start = radix_tree_next_hole(&mapping->page_tree, offset, max+1); - read_unlock_irq(&mapping->tree_lock); + rcu_read_lock(); + start = radix_tree_next_hole(&mapping->page_tree, offset+1,max); + rcu_read_unlock(); if (!start || start - offset > max) return 0; ra->start = start; ra->size = start - offset; /* old async_size */ + ra->size += req_size; ra->size = get_next_ra_size(ra, max); ra->async_size = ra->size; goto readit; } /* - * It may be one of - * - first read on start of file - * - sequential cache miss - * - oversize random read - * Start readahead for it. + * oversize read + */ + if (req_size > max) + goto initial_readahead; + + /* + * sequential cache miss */ + if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL) + goto initial_readahead; + + /* + * Query the page cache and look for the traces(cached history pages) + * that a sequential stream would leave behind. + */ + if (try_context_readahead(mapping, ra, offset, req_size, max)) + goto readit; + + /* + * standalone, small random read + * Read as is, and do not pollute the readahead state. + */ + return __do_page_cache_readahead(mapping, filp, offset, req_size, 0); + +initial_readahead: ra->start = offset; ra->size = get_init_ra_size(req_size, max); ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; readit: + /* + * Will this read hit the readahead marker made by itself? + * If so, trigger the readahead marker hit now, and merge + * the resulted next readahead window into the current one. + */ + if (offset == ra->start && ra->size == ra->async_size) { + ra->async_size = get_next_ra_size(ra, max); + ra->size += ra->async_size; + } + return ra_submit(ra, mapping, filp); } @@ -437,9 +517,10 @@ EXPORT_SYMBOL_GPL(page_cache_sync_readahead); * pagecache pages * * page_cache_async_ondemand() should be called when a page is used which - * has the PG_readahead flag: this is a marker to suggest that the application + * has the PG_readahead flag; this is a marker to suggest that the application * has used up enough of the readahead window that we should start pulling in - * more pages. */ + * more pages. + */ void page_cache_async_readahead(struct address_space *mapping, struct file_ra_state *ra, struct file *filp,